High side switch or low side switch

Discussion in 'General Electronics Chat' started by bug13, Jul 20, 2013.

  1. bug13

    Thread Starter Senior Member

    Feb 13, 2012
    1,233
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    hi guys

    I want to switch a mini RC servo off when it is not use in order to save power, should I use a high side switch or low side switch? I have tried low side switch, and haven't tried high side switch (as I don't have a P MOSFET at the moment).

    the low side switch seen to do weird thing. I haven't given much thought about these two different switch until I need to use it. Do I do something wrong here?

    Thanks guys!

    edit: according to the datasheet, at 3.3V gate voltage, the mosfet should give enough current to the for the servo.

    [​IMG]
     
  2. shortbus

    AAC Fanatic!

    Sep 30, 2009
    4,292
    2,205
    The low side is easier. But you have 6V available, why not use a driver and turn on a logic level mosfet fully? When you get away from the rated Vgs you will need a bigger heatsink for the mosfet. Because it will be operating in the resistive/linear region.
     
  3. bug13

    Thread Starter Senior Member

    Feb 13, 2012
    1,233
    40
    So function wise, there is no different for my application here(high side or low side)? My circuit works fine until I added a low side switch, and the servo seen to do weird thing that I don't expect it to do.

    I think I can get away without a heatsink but a reasonable copper pour, as my servo will only operate for 4-5 seconds then it will be at idle/switched off, that's my ideal anyway, is there any flaws?

    The reason that I don't want to use a mosfet driver is I want to maximize standby time/minimize standby current consumption. Do I still better off adding a mosfet driver? My goal is to have a standby current < 1mA.
     
  4. shortbus

    AAC Fanatic!

    Sep 30, 2009
    4,292
    2,205
    A high side switch definitely needs a driver of some sort. It needs to supply Vgs and drain voltage to work. A driver uses very little 'standby' current. Have a look at driver data sheets, there are many out there.
     
    bug13 likes this.
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